Unipolar acoustic pulse generator apparatus

ABSTRACT

In apparatus for producing a unipolar displacement of the radiating face of an electroacoustic transducer to generate unipolar accoustic pulses in an acoustic medium, the dimensions of the radiating face of the transducer or of an array of radiating transducer faces are chosen to simplify the response of the transducers, thereby simplifying the required transducer driving signals and the apparatus required to generate those signals.

United States Patent [1 1 Pepper UNIPOLAR ACOUSTIC PULSE GENERATORAPPARATUS [75] Inventor: Perry Arnold Pepper, Great Neck,

[2|] Appl. N0.: 354,519

[52] U.S. Cl 340/5 R; IMO/8.1; 340/10; 340/l5 [5 l] Int. Cl. H04b 11/008 Field of Search 340/3 A, 5 R, l0, l5;

[451 Apr. 22, 1975 3,7l5,7l0 2/l973 Bernstein et al 340/l5 X PrimaryExaminer-Richard A. Farley Attorney, Agent, or Firm-Daniel H. Steidl[57] ABSTRACT In apparatus for producing a unipolar displacement of theradiating face of an electroacoustic transducer to generate unipolaraccoustic pulses in an acoustic medium, the dimensions of the radiatingface of the transducer or of an array of radiating transducer faces arechosen to simplify the response of the transducers, thereby simplifyingthe required transducer driving signals and the apparatus required togenerate those signals.

[56] References Cited UNITED STATES PATENTS 50 Claims, 6 Drawing FiguresREP-RgTE 30 ei'ifim LOW PASS TRANSDUCER FILTER mammmzl 225% A&\. 1! J94AW-Z 2550 &'

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EPEFZmHmnEE UNIPOLAR ACOUSTIC PULSE GENERATOR APPARATUS BACKGROUND OFTHE INVENTION This invention relates to electroacoustic transducerapparatus and, more particularly, to eiectroacoustic transducerapparatus for producing high energy unipolar pressure pulses in anacoustic medium of relatively high specific impedance (e.g., water).

Unipolar acoustic pulses are useful in a wide variety of applications.In underwater sonar, for example, uni polar acoustic pulses radiatingfrom a transducer can be used for high resolution object detection,identification, and the like. Unipolar acoustic pulses are typicallygenerated by producing a unipolar displacement of the radiating face ofa transducer device (e.g., an electroacoustic transducer device) whichis immersed in or otherwise contiguous with an acoustic medium. Ingeneral, the unipolar displacement of the radiating transducer face(sometimes referred to herein as a unipolar transducer displacement orunipolar transducer response) results in a sequence of unipolar acousticpulses in the acoustic medium. The individual pulses in such a sequencedo not generally correspond to the amplitude and duration of theunipolar transducer displacement. Rather, the sequence of the acousticpulses usually corresponds more nearly to the second derivative of thedisplacement of the radiating transducer face (i.e., the accelerationhistory of the radiating transducer face). Unipolar transducerdisplacements are emdployed not because they uniquely result in unipolaracoustic pulses, but because the acoustic pulse sequences produced arerelatively uncomplicated and of short duration (i.e.. not substantiallylonger than the transducer displacement pulse). This latter feature isparticularly desirable for pulse repetition purposes. In reading thisspecification, the distinction between unipolar transducer displacementand unipolar acoustic pulses must be kept clearly in mind.

In copending U.S. patent application Ser. No. 92,798 now U.S. Pat. No.3,715,7l0, J. Bernstein, et al.. disclose apparatus for producingunipolar displacement of the radiating face of an electro-acoustictransducer. In accordance with the principles of that invention, atransducer (e..g., a cylindrical piezo-electric transducer) is driven byan electrical signal having discontinuities in amplitude which initiallystimulate vibration or mechanical oscillation of the transducer andthen, after a half cycle of transducer oscillation in the fundamentalmode. substantially dampen the oscillations of the transducer.Transducer oscillations are damped by applying signal discontinuities tothe transducer which would produce oscillations of the same amplitude asthe oscillations to be damped, but in phase opposition thereto, therebyinterfering with and tending to cancel out the undesired oscillations.Since transducers of the type described may exhibit more than one modeof vibration in each physical direction, it is appropriate to provide adriving signal having discontinuities for damping oscillation in severalof the more significant modes in order to produce a clean (i.e., sharplydefined) unipolar transducer response. In general, even for very simplyshaped transducer responses, the required driving voltage waveforms arequite complex and so will be the electrical or electronic apparatus usedto generate these waveforms.

In my concurrently filed application Ser. No. 354,5 l 8, it is shownthat for certain types of transducer responses, the transducer drivingsignal can be considerably simplified by relating the time parameter ofthe desired transducer response to the longitudinal dimension of thetransducer.

In certain situations it becomes necessary to consider the pressure ofthe acoustic medium on the radiating face of the transducer. This isparticularly true when the acoustic medium has a relatively high valueof specific impedance, as is true, for example, in the case of water. Inthat event. an additional driving signal component must be provided toaccount for the interaction of the transducer and the acoustic medium.

It is therefore an object of this invention to improve and simplifyunipolar acoustic pulse generating apparatus for use with acoustic mediaof relatively high specific impedance.

It is a more particular object ofthis invention to provide unipolaracoustic pulse generating apparatus in which the additional transducerdriving signal component required to account for the pressure of theacoustic medium on the radiating face of the transducer is simplifiedand the driving signal generating apparatus is also accordinglysimplified.

SUMMARY OF THE INVENTION These and other objects of the invention areaccomplished in accordance with the principles of the invention byunipolar acoustic pulse generator apparatus in which a certain dimensionof the radiating face of the transducer or of the several radiatingfaces of an array of transducers is chosen to simplify the response ofthe transducers, thereby simplifying the required driving signals andthe apparatus required to generate those signals. More particularly, thegreatest or principal dimension z of the radiating transducer face orarray of faces is chosen so that a time parameter I of the desiredunipolar acoustic output pulse is substantially equal to the quotientz/(,,-. where 0,, is the acoustic velocity of the ensonified acousticmedium.

Further features and objects of the invention, its nature and variousadvantages will be more apparent upon consideration of the attacheddrawing and the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. IA is a side view of apiezoelectric transducer of the type used for generating unipolaracoustic pulses in an acoustic medium;

FIG. 1B is an end view of the transducer of FIG. 1A;

FIG. 2A is a diagram of an idealized unipolar displacement of theradiating face of the transducer of FIG. I plotted against time;

FIG. 2B is a diagram of the additional transducer driving signalcomponent required to account for the pressure of the acoustic medium onthe radiating face of the transducer in unipolar acoustic pulsegenerator apparatus constructed in accordance with the principles ofthis invention;

FIG. 3 is a schematic block diagram of apparatus for generatingtransducer driving signals of the type shown in FIG. 2B; and

FIG. 4 is an end view of an array of transducers useful in understandingthe application of the principles of this invention to transducerarrays.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIGS. 1A and 18, atypical cylindrical electroacoustic transducer is made up of a pluralityof discs 12 interspersed with electrodes 14 and bonded together withadhesives or the like. Discs I2 are a piezoelectric material (e.g.,barium titanate or lead zirconate titanate) polarized to operate in the33 mode wherein the mechanical stresses in the transducer material areparallel to the longitudinal axis l6 of the transducer and perpendicularto the electrodes. Electrodes 14 are interconnected by wellknown wiringarrangements (not shown).

Transducer 10 has a radiating face I8 contiguous with an acoustic medium(e.g., air or water) and an op posite non-radiating face 20. Thenon-radiating face of transducer 10 is shown as free. but it may beclamped, attached to springs, or otherwise restrained in any manner.

When transducer 10 is energized by a suitable driving signal applied toelectrodes 14, radiating face 18 displaces, thereby projecting anacoustic signal into the surrounding acoustic medium. In manyapplications, the most desirable acoustic signal is a unipolar pulse. Asis discussed in greater detail in my above-mentioned concurrently filedapplication, unipolar acoustic pulses are most readily generated byproducing a unipolar displacement of the radiating face of thetransducer, as illustrated, for example, by the displacement history ofFIG. 2A. Although the particular displacement history shown in FIG. 2Ais not necessarily the most desirable in all applications and althoughthe principles of this invention are equally applicable to generating awide variety of other unipolar transducer responses, the presentinvention will be readily understood from an explanation of itsapplication to generating a trans ducer response of the type shown inFIG. 2A.

Apparatus for producing displacement of the radiat ing face of atransducer of the type shown in FIG. 1 is disclosed in theabove-mentioned application of Bernstein. et al., and in myabove-mentioned concurrently filed application. The required transducerdriving signal is typically a curved waveform having a number ofdiscontinuities for initially stimulating and then damping oscillationof the transducer. A driving signal of this type is convenientlygenerated by summing a plurality of appropriately shaped and timedsignal pulses. Appa ratus for generating a signal of this type is shownin FIG. 3. In the apparatus of FIG. 3, rep-rate signal generator anddifferentiator 32 produce a trigger signal whenever an acoustic outputpulse is required. This trigger signal is applied to each ofa pluralityof pulse generating signal channels, respectively represented by pulsegenerators 40-1 through 40-n. Each of pulse gen erators 40 produces anappropriately shaped and timed output signal pulse. The signal pulsesproduced by pulse generators 40 are scaled and summed by potentiometersS0 and operational amplifier 52 to produce a driving signal waveformapplied to transducer 70. If desired, the output signal of amplifier 52may be filtered by low pass filter 60 before being applied to transducer70. Signal generating apparatus of the type shown in FIG. 3, isdescribed in greater detail, for example, in my concurrently filedapplication.

As a rule, if the response of the transducer to driving signaldiscontinuities can be simplified, the quality of the acoustic outputpulse is improved and the number of modes of transducer oscillationrequiring damping is reduced. This results in simplification of therequired transducer driving signal and of the apparatus required togenerate that signal. As described in my concurrently filed application,a considerable simplification in the driving voltage waveform isachieved by designing the transducer so that the half pulse durationtime parameter t of the desired output pulse is an integer multiple ofthe quotient L/c, where L is the longitudinal dimension of thetransducer and c is the acoustic velocity of the material of thetransducer. The quotient U0 is a time parameter which corresponds to thetime required for an acoustic wave to propagate through the transduceralong its length L.

In certain applications, interaction between the ensonified acousticmedium and the transducer becomes a significant factor in transducerresponse. This is particularly true when acoustic pulses are to betransmitted into a medium, such as water, which has a relatively highspecific impedance value, this value being the product of the massdensity of the medium and its acoustic velocity c In that event, anadditional transducer driving signal component is required to accountfor the pressure of the medium on the radiating face of the transducer.While this additional signal component will in general have a distinctlysmaller amplitude than those signal components considered, for example,in my concurrently filed application, it must still be pres ent in thedriving signal waveform for accurate output pulse generation.

In general, the nature and complexity of the additional signal componentreferred to above depends on three time parameters: the half pulseduration time parameter l,,, the time required for an acoustic pulse totravel the length of the transducer (e.g., the quotient U0); and thetime required for an acoustic wave in the ensonified medium to traversethe greatest or principal dimension of the radiating face of thetransducer. The last of these parameters is given by the quotient z/cwhere z is the maximum dimension of the radiating face of the transducerand c is as defined above. As in my concurrently filed application, itis desirable for the purpose of simplifying this additional signalcomponent to design the transducer so that I is an interger multiple ofthe quotient L/(', the relationship t L/c being the most desirable. Inaccordance with the principles of the instant invention, it is alsodesirable for this purpose to design the transducer so that t (z/c,,.).The simplest additional signal component is required when both of theseconditions are met, i.e., when t (L/c) (ZICW).

In the case of the cylindrical transducer of FIG. 1, z is the diameterof radiating face 18. Assuming that t (Me) (2/0 for the transducer ofFIG. 1 and that non-radiating face 20 is not constrained, the additionaltransducer driving signal component required for the generation of theoutput pulse shown in FIG. 2A takes the form shown in FIG. 2B. Thiswaveform includes two pulses, each of duration t beginning respectivelyat l 0 and t 2! Each of these pulses includes an initial discontinuityfollowed by gradual decay. Between these two pulses, the signal waveformhas a polarity opposite that of the peaks of pulses. Like the othercomponents of the transducer driving signal, this additional drivingsignal component may be generated by one or more channels of theapparatus of FIG. 3, i.e., by one or more of pulse generators 40.

The principles discussed above in connection with cylindrical transducerof HG. l are equally applicable in a wide variety of other situations.In the case of an isolated cylindrical transducer of basic diameter doperating in the 33 mode and employing a circular radiating face ofdiameter d. it is d rather than d which should be used for z in thepreceding relationships. This situation is exemplified by many practicaltransducer designs employing end masses.

For an isolated prismatic transducer of any general cross sectionalshape operating in the 33 mode, is the maximum or greatest dimension ofthe radiating face. In the case of a transducer having a square orrectangular radiating face. for example, z is the diagonal of the squareor rectangle. [n the case of a transducer having a triangular radiatingface, 2 is the longest side of the triangle. ln the case of a transducerhaving an elliptical radiating face, 2 is the major axis of the ellipse.

In certain applications, it may be desired to produce transducerresponses having different durations. For example, such responses mayall have the form shown in FIG. 2A, but with different values of t aswell as different amplitudes. in accordance with the foregoingprinciples of this invention. this capability is best achieved by use ofa single transducer for each different response duration. Eachtransducer would then have a different radiating face dimension, 2. inaccordance with the optimizing principle, 1 =c,.r,,, and, in accordancewith the optimizing principle disclosed in my above-mentionedconcurrently filed application, i.e.. L cl would have a differentlength, L.

The principles of this invention are also applicable to arrays oftransducers having multiple radiating faces in a common plane. in thecase ofsuch an array, the maximum dimension of the array of radiatingfaces corresponds to the maximum dimension of the radiating face of anisolated transducer and is the value of z in the relationships above.For the rectangular array of radiating faces 80 shown in FIG. 4, z isthe diagonal of the array as indicated by the segment a b. As is evidentfrom this example, the intervening portions of the nonradiatinginterstices 82 between the radiating faces 80 must be included indetermining the distance 2.

What is claimed is:

1. Apparatus for producing a unipolar displacement of the radiating faceof an electroacoustic transducer to produce an acoustic signal in amedium having an acoustic velocity c said unipolar displacement having ahalf pulse duration time parameter r, and said radiating face havingmaximum dimenion z, characterized in that 1,, is substantially equal tothe quotient (z/c means for generating a signal waveform, and means forapplying said signal waveform to said transducer.

2. Apparatus for producing a unipolar displacement of the radiating faceof an electroacoustic transducer to produce an acoustic signal in amedium having an acoustic velocity c... said unipolar displacementhaving a half pulse duration time parameter r, and said radiating facehaving maximum dimension z, characterized in that t, is substantiallyequal to the quotient (z/c,,.) said radiating face of said transducerdisplacing from a rest position to maximum displacement during during afirst interval of time t and returning from maximum displacement to saidrest position during a second subsequent interval of time t and meansfor applying to said transducer an electrical signal including a signalcomponent characterized by a first signal pulse at the start of saidfirst time interval and a second signal pulse at the end of said secondtime interval.

3. The apparatus defined in claim 2 wherein each of said signal pulsesis characterized by a substantially instantaneous rise time followed bygradual decay.

4. The apparatus defined in claim 3 wherein the rise time of said firstsignal pulse is substantially concurrent with the start of said firsttime interval and the rise time of said second signal pulse issubstantially concurrent with the end of said second time interval.

5. The apparatus defined in claim 4 wherein the duration of each of saidsignal pulses is substantially equal to r,,.

6. The apparatus defined in claim 5 wherein said electrical signalcomponent is further characterized by a predetermined reference signallevel before said first signal pulse and after said second signal pulse.

7. The apparatus defined in claim 6 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.

8. The apparatus defined in claim 7 wherein said electrical signalcomponent is further characterized by a polarity opposite said firstpolarity during the interval of time between said first and secondsignal pulses.

9. The apparatus defined in claim 8 wherein the radiating face of saidtransducer is a circular surface of diameter z.

10. The apparatus defined in claim 9 wherein said transducer is acylinder, one end of which is the radiating face of said transducer.

11. The apparatus defined in claim 8 wherein the radiating face of saidtransducer is a rectangle of diagonal z.

12. The apparatus defined in claim 8 wherein the radiating face of saidtransducer is a triangle having longest side 2.

13. The apparatus defined in claim 8 wherein the radiating face of saidtransducer is an ellipse having major axis 2.

14. The apparatus defined in claim 2 wherein said means for applyingcomprises:

means for generating a trigger signal;

a plurality of shaped pulse generating channels responsive to saidtrigger signal, each of said channels comprising means for delaying saidtrigger sig nal. means responsive to the delayed trigger signal forgenerating a rectangular pulse of predetermined amplitude and duration,and means for shaping said rectangular pulse to produce a shaped outputpulse; and

means for summing the shaped output pulses of each of said channels toproduce said electrical signal.

15. Apparatus for producing a unipolar displacement of the radiatingface of an electroacoustic transducer to produce an acoustic signal in amedium having an acoustic velocity c... said unipolar displacementhaving a half pulse duration time parameter I, and said radiating facehaving a maximum dimension 1. characterized in that r, is substantiallyequal to the quotient (z/cw), said transducer being characterized by anacoustic velocity r, wherein the dimension L of said transducer normalto said radiating face bears substantially the same proportionalrelation to c as 2 bears to c... and wherein the radiating face of saidtransducer displaces from a rest position to maximum displacement duringa first interval of time r, and returns from maximum displacement tosaid rest during a second subsequent interval of time i means forapplying to said transducer an electrical signal including a signalcomponent characterized by a first signal pulse at the start of saidfirst time interval and a second signal pulse at the end of said secondtime interval.

16. The apparatus defined in claim wherein each of said signal pulses ischaracterized by a substantially instantaneous rise time followed bygradual decay.

T7. The apparatus defined in claim 16 wherein the rise time of saidfirst pulse is substantially concurrent with the start of said firsttime interval and the rise time of said second signal pulse issubstantially concurrent with the end of said second time interval.

18. The apparatus defined in claim 17 wherein the duration of each ofsaid signal pulses is substantially equal to t 19. The apparatus definedin claim 18 wherein said electrical signal component is furthercharacterized by a predetermined reference signal level before saidfirst signal pulse and after said second signal pulse.

20. The apparatus defined in claim l9 wherein the peaks of both of saidsignal pulses are the first polarity relative to said predeterminedreference signal level.

21. The apparatus defined in claim 20 wherein said electrical signalcomponent is further characterized by a polarity opposite said firstpolarity during the interval of time between said first and secondsignal pulses.

22. The apparatus defined in claim 21 wherein the radiating face of saidtransducer is a circular surface of diameter 23. The apparatus definedin claim 22 wherein said transducer is a cylinder of length L. one endof which is the radiating face of said transducer.

24. The apparatus defined in claim 15 wherein said means for applyingcomprises:

means for generating a trigger signal;

a plurality of shaped pulse generating channels responsive to saidtrigger signal. each of said channels comprising means for delaying saidtrigger signal. means responsive to the delayed trigger signal forgenerating a rectangular pulse of predetermined amplitude and duration,and means for shaping said rectangular pulse to produce a shaped outputpulse. and

means for summing the shaped output pulses of each of said channels toproduce said electrical signal.

25. Apparatus for producing a unipolar displacement of the radiatingface of an electroacoustic transducer to produce an acoustic signal in amedium having an acoustic velocity 0,... the radiating face of saidtransducer having maximum dimension 2 and said transducer having anacoustic velocity and a dimension L normal to said radiating face,wherein the ratio of z to c is substantially equal to the ratio of L toc, means for generating a signal waveform, and means for applying saidsignal waveform to said transducer.

26. Apparatus for producing a unipolar displacement of the radiatingface of an electroacoustic transducer to produce an acoustic signal in amedium characterized by an acoustic velocity c,,. said unipolardisplacement having a half pulse duration time parameter t the radiatingface of said transducer having maximum dimension 2. and said transducerhaving an acoustic velocity c and a dimension L normal to said radiatingface, wherein I is substantially equal to the quotient (Mr) and to thequotient (z/c means for generating a signal waveform, and means forapplying said signal waveform to said transducer.

27. Apparatus for producing a unipolar displacement of the radiatingface of an electroacoustic transducer to produce an acoustic signal inan acoustic medium, said unipolar displacement having a half pulseduration time parameter t characterized in that t is substantially equalto the time required for an acoustic wave to traverse the maximumdimension of the radiating face through the acoustic medium, means forgenerating a signal waveform, and means for applying said signalwaveform to said transducer.

28. Apparatus for producing a unipolar displacement of the radiatingface of an electroacoustic transducer to produce an acoustic signal inan acoustic medium, said transducer having a non-radiating face oppositesaid radiating face. said unipolar displacement having a half pulseduration time parameter 1 characterized in that 1,, is substantiallyequal to the time required for an acoustic wave to travel through thetransducer from one face to the other and further characterized in thatI is substantially equal to the time required for an acoustic wave totraverse the maximum dimension of the radiating face through theacoustic medium, means for generating a signal waveform, and means forapplying said signal waveform to said transducer.

29. Apparatus for generating a unipolar displacement of the radiatingfaces of a plurality of electroacoustic transducers to produce anacoustic signal in a medium having an acoustic velocity c said unipolardisplacement having a half pulse duration time parameter t the radiatingfaces of said transducers forming a coplanar array having a maximumdimension 2 characterized in that 1,, is substantially equal to thequotient (LI/C means for generating a signal waveform. and means forapplying said signal waveform to said transducers.

30. The apparatus defined in claim 29 wherein the radiating faces ofsaid transducers displace from a rest position to maximum displacementduring a first interval of time t and return from maximum displacementto said rest position during a second subsequent interval of time t,,.

31. The apparatus defined in claim 29 wherein each of said transducersis characterized by an acoustic velocity c and wherein the dimension Lof each of said transducers normal to its radiating face bearssubstantially the same proportional relation to c as z bears to 32. Theapparatus defined in claim 31 wherein the radiating faces of saidtransducers displace from a rest position to maximum displacement duringa first interval of time 1., and return from maximum displacement tosaid rest position during a second subsequent interval of time t,,.

33. The apparatus defined in claim 32 comprising means for applying tosaid transducers an electrical signal including a signal componentcharacterized by a first signal pulse at the start of said first timeinterval and a second signal pulse at the end of said second timeinterval.

34. The apparatus defined in claim 33 wherein each of said signal pulsesis characterized by a substantially instantaneous rise time followed bygradual decay.

35. The apparatus defined in claim 34 wherein the rise time of saidfirst signal pulse is substantially concurrent with the start of saidfirst time interval and the rise time of said second signal pulse issubstantially concurrent with the end of said second time interval.

36. The apparatus defined in claim 35 wherein the duration of each ofsaid signal pulses is substantially equal to l,,.

37. The apparatus defined in claim 36 wherein said electrical signalcomponent is further characterized by a predetermined reference signallevel before said first signal pulse and after said second signal pulse.

38. The apparatus defined in claim 37 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.

39. The apparatus defined in claim 38 wherein said electrical signalcomponent is further characterized by a polarity opposite said firstpolarity during the interval of time between said first and secondsignal pulses.

40. The apparatus defined in claim 33 wherein said means for applyingcomprises:

means for generating a trigger signal;

a plurality of shaped pulse generating channels responsive to saidtrigger signal. each of said channels comprising means for delaying saidtrigger signal for generating a rectangular pulse of predeterminedamplitude and duration, and means for shaping said rectangular pulse toproduce a shaped output pulse; and

means for summing the shaped output pulses of each of said channels toproduce said electrical signal.

41. Apparatus for producing a unipolar displacement of the radiatingfaces of a plurality of electroacoustic transducers to produce anacoustic signal in a medium having an acoustic velocity c said unipolardisplacement having a half pulse duration time parameter I the radiatingfaces of said transducers forming a coplanar array having a maximumdimension z, each of said transducers having an acoustic velocity r" anda dimension L perpendicular to its radiating face. wherein 1,, issubstantially equal to the quotient (U) and to the quotient means forgenerating a signal waveform, and means for applying said signalwaveform to said transducers.

42. Apparatus for producing a unipolar displacement of the radiatingfaces of a plurality of electroacoustic transducers to produce anacoustic signal in an acoustic medium, said unipolar displacement havinga half pulse duration time parameter t the radiating faces of saidtransducers forming a coplanar array having a maximum dimension z. eachof said transducers having a non-radiating face opposite said radiatingface, characterized in that I, is substantially equal to the timerequired for an acoustic wave to propagate through each of saidtransducers from one of its faces to the other and further characterizedin that 1., is substantially equal to the time required for an acousticwave to prop agate a distance 1 in the acoustic medium, means forgenerating a signal waveform, and means for applying said signalwaveform to said transducers.

43. Apparatus for generating a unipolar acoustic displacement of theradiating faces of a plurality of electroacoustic transducers, toproduce an acoustic signal in a medium having an acoustic velocity csaid unipolar displacement having a half pulse duration time parameter rthe radiating faces of said transducers forming a coplanar array havinga maximum dimension z characterized in that r, is substantially equal tothe quotient (zlc the radiating faces of said transducers displacingfrom a rest position to maximum displacement during a first interval oftime t and returning from maximum displacement to said rest positionduring a second subsequent interval of time t and means for applying tosaid transducers an electrical signal including a signal componentcharacterized by a first signal pulse at the start of said first timeinterval and a second signal pulse at the end of said second timeinterval.

44. The apparatus defined in claim 43 wherein each of said signal pulsesis characterized by a substantially instantaneous rise time followed bygradual decay.

45. The apparatus defined in claim 44 wherein the rise time of saidfirst signal pulse is substantially con current with the start of saidfirst time interval and the rise time of said second signal pulse issubstantially concurrent with the end of said second time interval.

46. The apparatus defined in claim 45 wherein the duration of each ofsaid signal pulses is substantially equal to t 47. The apparatus definedin claim 46 wherein said electrical signal component is furthercharacterized by a predetermined reference signal level before saidfirst signal pulse and after said second signal pulse.

48. The apparatus defined in claim 47 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.

49. The apparatus defined in claim 48 wherein said electrical signalcomponent is further characterized by a polarity opposite said firstpolarity during the interval of time between said first and secondsignal pulses.

50. The apparatus defined in claim 43 wherein said means for applyingcomprises:

means for generating a trigger signal;

a plurality of shaped pulse generating channels responsive to saidtrigger signal, each of said channels comprising means for delaying saidtrigger signal, means responsive to the delayed trigger signal forgenerating a rectangular pulse of predetermined amplitude and duration,and means for shaping said rectangular pulse to produce a shaped outputpulse; and

means for summing the shaped output pulses of each of said channels toproduce said electrical signal.

1. Apparatus for producing a unipolar displacement of the radiating faceof an electroacoustic transducer to produce an acoustic signal in amedium having an acoustic velocity cw, said unipolar displacement havinga half pulse duration time parameter to and said radiating face havingmaximum dimenion z, characterized in that to is substantially equal tothe quotient (z/cw), means for generating a signal waveform, and meansfor applying said signal waveform to said transducer.
 2. Apparatus forproducing a unipolar displacement of the radiating face of anelectroacoustic transducer to produce an acoustic signal in a mediumhaving an acoustic velocity cw, said unipolar displacement having a halfpulse duration time parameter to and said radiating face having maximumdimension z, characterized in that to is substantially equal to thequotient (z/cw), said radiating face of said transducer displacing froma rest position to maximum displacement during during a first intervalof time to and returning from maximum displacement to said rest positionduring a second subsequent interval of time to, and means for applyingto said transducer an electrical signal including a signal componentcharacterized by a first signal pulse at the start of said first timeinterval and a second signal pulse at the end of said second timeinterval.
 3. The apparatus defined in claim 2 wherein each of saidsignal pulses is characterized by a substantially instantaneous risetime followed by gradual decay.
 4. The apparatus defined in claim 3wherein the rise time of said first signal pulse is substantiallyconcurrent with the start of said first time interval and the rise timeof said second signal pulse is substantially concurrent with the end ofsaid second time interval.
 5. The apparatus defined in claim 4 whereinthe duration of each of said signal pulses is substantially equal to to.6. The apparatus defined in claim 5 wherein said electrical signalcomponent is further characterized by a predetermined reference signallevel before said first signal pulse and after said second signal pulse.7. The apparatus defined in claim 6 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.
 8. The apparatus defined in claim 7 wherein saidelectrical signal component is further characterized by a polarityopposite said first polarity during the interval of time between saidfirst and second signal pulses.
 9. The apparatus defined in claim 8wherein the radiating face of said transducer is a circular surface ofdiameter z.
 10. The apparatus defined in claim 9 wherein said transduceris a cylinder, one end of which is the radiating face of saidtransducer.
 11. The apparatus defined in claim 8 wherein the radiatingface of said transducer is a rectangle of diagonal z.
 12. The apparatusdefined in claim 8 wherein the radiating face of said transducer is atriangle having longest side z.
 13. The apparatus defined in claim 8wherein the radiating face of said transducer is an ellipse having majoraxis z.
 14. The apparatus defined in claim 2 wherein said means forapplying comprises: means for generating a trigger signal; a pluralityof shaped pulse generating channels responsive to said trigger signal,each of said channels comprising means for delaying said trigger signal,means responsive to the delayed trigger signal for generating arectangular pulse of predetermined amplitude and duration, and means forshaping said rectangular pulse to produce a shaped output pulse; andmeans for summing the shaped output pulses of each of said channels toproduce said electrical signal.
 15. Apparatus for producing a unipolardisplacement of the radiating face of an electroacoustic transducer toproduce an acoustic signal in a medium having an acoustic velocity cw,said unipolar displacement having a half pulse duration time parameterto and said radiating face having a maximum dimension z, characterizedin that to is substantially equal to the quotient (z/cw), saidtransducer being characterized by an acoustic velocity c, wherein thedimension L of said transducer normal to said radiating face bearssubstantially the same proportional relation to c as z bears to cw, andwherein the radiating face of said transducer displaces from a restposition to maximum displacement during a first interval of time to andreturns from maximum displacement to said rest during a secondsubsequent interval of time to, means for applying to said transducer anelectrical signal including a signal component characterized by a firstsignal pulse at the start of said first time interval and a secondsignal pulse at the end of said second time interval.
 16. The apparatusdefined in claim 15 wherein each of said signal pulses is characterizedby a substantially instantaneous rise time followed by gradual decay.17. The apparatus defined in claim 16 wherein the rise time of saidfirst pulse is substantially concurrent with the start of said firsttime interval and the rise time of said second signal pulse issubstantially concurrent with the end of said second time interval. 18.The apparatus defined in claim 17 wherein the duration of each of saidsignal pulses is substantially equal to to.
 19. The apparatus defined inclaim 18 wherein said electrical signal component is furthercharacterized by a predetermined reference signal level before saidfirst signal pulse and after said second signal pulse.
 20. The apparatusdefined in claim 19 wherein the peaks of both of said signal pulses arethe first polarity relative to said predetermined reference signallevel.
 21. The apparatus defined in claim 20 wherein said electricalsignal component is further characterized by a polarity opposite saidfirst polarity during the interval of time between said first and secondsignal pulses.
 22. The apparatus defined in claim 21 wherein theradiating face of said transducer is a circular surface of diameter z.23. The apparatus defined in claim 22 wherein said transducer is acylinder of length L, one end of which is the radiating face of saidtransducer.
 24. The apparatus defined in claim 15 wherein said means forapplying comprises: means for generating a trigger signal; a pluralityof shaped pulse generating channels responsive to said trigger signal,Each of said channels comprising means for delaying said trigger signal,means responsive to the delayed trigger signal for generating arectangular pulse of predetermined amplitude and duration, and means forshaping said rectangular pulse to produce a shaped output pulse; andmeans for summing the shaped output pulses of each of said channels toproduce said electrical signal.
 25. Apparatus for producing a unipolardisplacement of the radiating face of an electroacoustic transducer toproduce an acoustic signal in a medium having an acoustic velocity cw,the radiating face of said transducer having maximum dimension z andsaid transducer having an acoustic velocity c and a dimension L normalto said radiating face, wherein the ratio of z to cw is substantiallyequal to the ratio of L to c, means for generating a signal waveform,and means for applying said signal waveform to said transducer. 26.Apparatus for producing a unipolar displacement of the radiating face ofan electroacoustic transducer to produce an acoustic signal in a mediumcharacterized by an acoustic velocity cw, said unipolar displacementhaving a half pulse duration time parameter to, the radiating face ofsaid transducer having maximum dimension z, and said transducer havingan acoustic velocity c and a dimension L normal to said radiating face,wherein to is substantially equal to the quotient (L/c) and to thequotient (z/cw), means for generating a signal waveform, and means forapplying said signal waveform to said transducer.
 27. Apparatus forproducing a unipolar displacement of the radiating face of anelectroacoustic transducer to produce an acoustic signal in an acousticmedium, said unipolar displacement having a half pulse duration timeparameter to, characterized in that to is substantially equal to thetime required for an acoustic wave to traverse the maximum dimension ofthe radiating face through the acoustic medium, means for generating asignal waveform, and means for applying said signal waveform to saidtransducer.
 28. Apparatus for producing a unipolar displacement of theradiating face of an electroacoustic transducer to produce an acousticsignal in an acoustic medium, said transducer having a non-radiatingface opposite said radiating face, said unipolar displacement having ahalf pulse duration time parameter to, characterized in that to issubstantially equal to the time required for an acoustic wave to travelthrough the transducer from one face to the other and furthercharacterized in that to is substantially equal to the time required foran acoustic wave to traverse the maximum dimension of the radiating facethrough the acoustic medium, means for generating a signal waveform, andmeans for applying said signal waveform to said transducer. 29.Apparatus for generating a unipolar displacement of the radiating facesof a plurality of electroacoustic transducers to produce an acousticsignal in a medium having an acoustic velocity cw, said unipolardisplacement having a half pulse duration time parameter to, theradiating faces of said transducers forming a coplanar array having amaximum dimension z characterized in that to is substantially equal tothe quotient (z/cw), means for generating a signal waveform, and meansfor applying said signal waveform to said transducers.
 30. The apparatusdefined in claim 29 wherein the radiating faces of said transducersdisplace from a rest position to maximum displacement during a firstinterval of time to and return from maximum displacement to said restposition during a second subsequent interval of time to.
 31. Theapparatus defined in claim 29 wherein each of said transducers ischaracterized by an acoustic velocity c and wherein the dimension L oFeach of said transducers normal to its radiating face bearssubstantially the same proportional relation to c as z bears to cw. 32.The apparatus defined in claim 31 wherein the radiating faces of saidtransducers displace from a rest position to maximum displacement duringa first interval of time to and return from maximum displacement to saidrest position during a second subsequent interval of time to.
 33. Theapparatus defined in claim 32 comprising means for applying to saidtransducers an electrical signal including a signal componentcharacterized by a first signal pulse at the start of said first timeinterval and a second signal pulse at the end of said second timeinterval.
 34. The apparatus defined in claim 33 wherein each of saidsignal pulses is characterized by a substantially instantaneous risetime followed by gradual decay.
 35. The apparatus defined in claim 34wherein the rise time of said first signal pulse is substantiallyconcurrent with the start of said first time interval and the rise timeof said second signal pulse is substantially concurrent with the end ofsaid second time interval.
 36. The apparatus defined in claim 35 whereinthe duration of each of said signal pulses is substantially equal to to.37. The apparatus defined in claim 36 wherein said electrical signalcomponent is further characterized by a predetermined reference signallevel before said first signal pulse and after said second signal pulse.38. The apparatus defined in claim 37 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.
 39. The apparatus defined in claim 38 whereinsaid electrical signal component is further characterized by a polarityopposite said first polarity during the interval of time between saidfirst and second signal pulses.
 40. The apparatus defined in claim 33wherein said means for applying comprises: means for generating atrigger signal; a plurality of shaped pulse generating channelsresponsive to said trigger signal, each of said channels comprisingmeans for delaying said trigger signal for generating a rectangularpulse of predetermined amplitude and duration, and means for shapingsaid rectangular pulse to produce a shaped output pulse; and means forsumming the shaped output pulses of each of said channels to producesaid electrical signal.
 41. Apparatus for producing a unipolardisplacement of the radiating faces of a plurality of electroacoustictransducers to produce an acoustic signal in a medium having an acousticvelocity cw, said unipolar displacement having a half pulse durationtime parameter to, the radiating faces of said transducers forming acoplanar array having a maximum dimension z, each of said transducershaving an acoustic velocity c and a dimension L perpendicular to itsradiating face, wherein to is substantially equal to the quotient (L/c)and to the quotient (z/cw), means for generating a signal waveform, andmeans for applying said signal waveform to said transducers. 42.Apparatus for producing a unipolar displacement of the radiating facesof a plurality of electroacoustic transducers to produce an acousticsignal in an acoustic medium, said unipolar displacement having a halfpulse duration time parameter to, the radiating faces of saidtransducers forming a coplanar array having a maximum dimension z, eachof said transducers having a non-radiating face opposite said radiatingface, characterized in that to is substantially equal to the timerequired for an acoustic wave to propagate through each of saidtransducers from one of its faces to the other and further characterizedin that to is substantially equal to the time required for an acousticwave to propagate a distance z in the acoustic medium, means forgenerating a signal waveform, And means for applying said signalwaveform to said transducers.
 42. Apparatus for producing a unipolardisplacement of the radiating faces of a plurality of electroacoustictransducers to produce an acoustic signal in an acoustic medium, saidunipolar displacement having a half pulse duration time parameter to,the radiating faces of said transducers forming a coplanar array havinga maximum dimension z, each of said transducers having a non-radiatingface opposite said radiating face, characterized in that to issubstantially equal to the time required for an acoustic wave topropagate through each of said transducers from one of its faces to theother and further characterized in that to is substantially equal to thetime required for an acoustic wave to propagate a distance z in theacoustic medium, means for generating a signal waveform, And means forapplying said signal waveform to said transducers.
 43. Apparatus forgenerating a unipolar acoustic displacement of the radiating faces of aplurality of electroacoustic transducers, to produce an acoustic signalin a medium having an acoustic velocity cw, said unipolar displacementhaving a half pulse duration time parameter to, the radiating faces ofsaid transducers forming a coplanar array having a maximum dimension zcharacterized in that to is substantially equal to the quotient (z/cw),the radiating faces of said transducers displacing from a rest positionto maximum displacement during a first interval of time to and returningfrom maximum displacement to said rest position during a secondsubsequent interval of time to, and means for applying to saidtransducers an electrical signal including a signal componentcharacterized by a first signal pulse at the start of said first timeinterval and a second signal pulse at the end of said second timeinterval.
 44. The apparatus defined in claim 43 wherein each of saidsignal pulses is characterized by a substantially instantaneous risetime followed by gradual decay.
 45. The apparatus defined in claim 44wherein the rise time of said first signal pulse is substantiallyconcurrent with the start of said first time interval and the rise timeof said second signal pulse is substantially concurrent with the end ofsaid second time interval.
 46. The apparatus defined in claim 45 whereinthe duration of each of said signal pulses is substantially equal to to.47. The apparatus defined in claim 46 wherein said electrical signalcomponent is further characterized by a predetermined reference signallevel before said first signal pulse and after said second signal pulse.48. The apparatus defined in claim 47 wherein the peaks of both of saidsignal pulses are of a first polarity relative to said predeterminedreference signal level.
 49. The apparatus defined in claim 48 whereinsaid electrical signal component is further characterized by a polarityopposite said first polarity during the interval of time between saidfirst and second signal pulses.